While I do not agree it should be blocked, it would be a lie, as falloutdude said, to say that not a lot of players die during that time. The guards that are usually at the spawn points also go into the swarm, allowing all the plasma-grenadiers to come in and kill everyone. But it's all just petty NCR stuff, not like it really matters (though in this case, NCR seems to be the only city still alive).